1. Field of the Invention
This invention relates to methods and devices for balancing colors in optical camera systems. More particularly, the invention relates to a device and method for white-balancing video cameras used in surgical procedures. Still more particularly, the invention relates to white balancing video cameras used in endoscopic surgical procedures.
2. Description of the Prior Art
While the invention generally relates to white-balancing any video camera, it has particular utility for use with video cameras adapted for surgical endoscopic procedures utilizing cameras, internal illumination sources and external monitors. In such procedures it is important that camera systems portray accurate colors as much as possible since colors of internal organs are often indicative of their physiological condition and since surgeons must totally rely on the image presented to them on a monitor in order to make a proper diagnosis.
As used herein, the term "endoscopic" is used to mean all least invasive medical procedures such as arthroscopy, laparoscopy, etc. in which a camera is used to visualize internal. parts of a body through small body openings (either artificially created or naturally occurring). The terms "endoscope" and "scope" are used to refer to the cameras used in such procedures, such cameras having elongated optics-containing tubes between the distal (objective) tip and the proximal, image-forming components. The invention described herein is suitable for use with a variety of scope configurations and also with scopes which may have the image forming components at the distal tip. Such cameras are generally used with fiber optics situated in the elongated tube to direct light from an external light source to the internal work site being viewed by the camera. It is this light, reflected from internal organs, which illuminates the scene viewed by the surgeon.
In order for the video equipment to perform optimally, it must be white balanced. White balancing a camera predefines what the color white will be for a particular camera. That is, the camera's output is adjusted to "white" when a selected white target is viewed. If white balancing is improperly performed, the video picture presented on the monitor will not truly represent the image viewed by the camera.
Operating room personnel and surgeons typically white balance a camera using highly subjective (and, therefore, variable) techniques such as aiming the camera at a target such as 4".times.4" piece of gauze, styrofoam cup, paper or other white surface. These techniques all involve focusing the scope onto the white surface by holding the scope an appropriate distance from the white surface to enable it to receive light reflected from the surface while simultaneously adjusting the light intensity of the light source. The camera white balancing button is then depressed when the camera operator feels the picture on the monitor is not blooming or oversaturated with light and represents a true white color or good brightness. The manner in which the camera electronics are adjusted forms no part of this invention.
The current methods of white balancing a camera are very subjective and leave room for error. Disadvantages of these techniques involve the inaccuracies created by using reflective surfaces and the difficulty of being able to steadily hold a scope at an optimum distance from a target. Since the camera light source is effectively at the scope tip, reliance on the reflective properties of a surface for white balancing results in the center of the picture being much brighter than the edges, thus producing an uneven brightness across the image on the monitor. Also, inconsistencies in the surface at which the scope is aimed can cause shadowing and dark spots resulting in poor picture quality. Furthermore, textural features on the surface create color and brightness variations in the image used to form the basis of the white balance, thus resulting in an inaccurate adjustment. Additionally, it is difficult for a user to hold the scope the ideal distance away from the white surface while trying to adjust the light source intensity level and depress the white balance button at the same time.